This was the highest tally since data collection started in 2001 and a jump of 54% compared with the previous year.

The Home Office said the increase was partly due to a large number of arrests made following terrorist attacks in London and Manchester.

The 400 total includes 64 arrests made in connection with the Westminster (12), Manchester (23), London Bridge (21), Finsbury Park (one) and Parsons Green (seven) attacks.

The figures show that of the arrests made over the year: 115 (29%) resulted in a charge, of which 97 (84%) were charged with terrorism-related offences; 213 (53%) were released without charge; 60 (15%) were released on bail pending further investigation; 11 (3%) faced “alternative action”; and one case was pending.

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Of those held, a record 58 were female, and 18 were aged under 18.

Police officers guard the gates to Downing Street in London (Picture: AP)

There were year-on-year increases in the number of arrests across all ethnic groups, including a 77% rise in the number of white suspects held, from 81 to 143.

The figures show an annual jump of more than a third in arrests linked to international terrorism, from 212 to 292.

Yesterday, it was revealed that MI5 have thwarted a total of nine terror attacks on British soil in the last year.

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Andrew Parker told Theresa May and her senior ministers that the defeat of Islamic State in Iraq and Syria did not mean the terror threat was over, warning that social media was being used to encourage attacks in the UK and elsewhere.

Home Secretary Amber Rudd told the weekly meeting in 10 Downing Street that the pace of attack planning has increased ‘significantly’ over the past year.

Mrs May told ministers that the threat from terror was at an ‘unprecedented’ level, despite the military setbacks experienced in its Middle East strongholds by Islamic State – also known as Daesh.